The early '70s was when the hardware of computers began to scale down while the market began to explode. You had mainframes, which were the big rack-mounted machines. Then, some companies came out with what they called minicomputers. Also rack-mounted, but more of the components were consolidated. These were generally 16-bit machines.
The first machine I worked on was the DEC PDP-11/05, in '77. I was in jr high at the time, and my mom wouldn't allow my dad to set the machine up in the house. So, it was in the garage. In Texas. Many days it was too hot or too cold to run. The CPU in that machine, just the CPU, was the size of today's desktop computers. Ours had 48k words of memory, and two 2 MB hard drives. We had to use paper tape for diagnostics, when the machine had problems. Later, he added another two hard drives, and dual 8" floppies.
Then came the microcomputers. These were usually 8-bit machines, that used Large Scale Integration (LSI,) to put the entire CPU onto a single chip. The first commercially available LSI chip was the Intel 4004. That was upgraded to the 8008, then 8080. That was considered a solid design, and there were several kit computers, and a few turnkey systems based around it. The 8080 was cloned and extended by Zilog and released as the Z80, which was even more popular.
Intel then made some evolutionary changes to create the 8086 and 8088 families of CPUs. These were sort of hybrid 8-bit and 16-bit CPUs. They had 8-bit registers, but they could be paired up for certain functions to make 16 bits. The memory addressing was essentially 12-bit. They were still referred to as microcomputers. I think mostly because of the LSI packaging.
Microsoft never ran Windows on the 8080. They did have a version of the BASIC language that ran on some of the early microprocessors. I know it ran on a Z80, It probably ran on some 8080 boxes, because the architecture of the CPU was very similar.
Then, Microsoft landed the deal to provide the operating system for the 8088-based IBM PC. They purchased a company that had an operating system already written for that CPU, and customized it for IBM. But, they were savvy enough to retain the rights to sell it widely. That was the start of PC-DOS and MS-DOS.
Windows 1.0 through 3.0 ran on 8086/8088 hardware. I tried a copy of v1.0 for a day or two. It didn't run very well, but it did run. By the time of v1.0, the 80286 was out, which, of course, was a lot faster.. By the time of v3.0, the 80386 was available. Microsoft then tweaked Windows a little to take advantage of some of the features of the 80386, and released Windows 3.1. Most consider that the first really viable version of Windows.
By this time, the Mac had been around for a few years. And so on.